High levels of brain natriuretic
peptide (BNP) in heart failure patients is a warning
sign of mortal danger ahead, according to a study in
the May 15 issue of the Journal of the American College
of Cardiology. The authors suggest a simple blood
test at hospital admission would help doctors provide
better care by triaging heart failure patients according
to their BNP levels and tailoring their treatment choices.
BNP is released by the heart in
response to ventricle wall tension, and decreases blood
volume. Researchers looked at data from over 48,000
heart failure patients and found a surprisingly direct
correlation between high levels of BNP and increased
in-hospital mortality risk.
"What was remarkable and surprising
to us was how well the BNP blood test performed, with
a near linear relationship between [BNP level] quartiles
and in-hospital mortality," says lead author Dr Gregg
C Fonarow, a cardiologist at UCLA. "Furthermore, this
was independent of other validated and well-known risk
predictors for mortality," he adds, naming age, gender,
systolic blood pressure, pulse and other lab tests,
including blood urea nitrogen, creatinine and sodium.
"Our study provides clinicians
with additional information about their patients. Patients
in the lowest quartile, despite being hospitalized for
acute decompensated heart failure, had a less than 2%
mortality rate, while for patients in the highest quartile,
the mortality rate was three-fold higher, at 6%. This
helps clinicians identify patients who need more monitoring
and therapy, whereas patients at lower risk can be successfully
managed in a less intensive hospital setting," says
Dr Fonarow.
WELCOME
TEST
Dr Fonarow and his colleagues used data from the US
Acute Decompensated Heart Failure National Registry,
which contains the largest set of heart failure data
in the world. The researchers looked at the 48,629 heart
failure patients whose BNP levels were taken within
24 hours of hospital admission, between April 2003 and
December 2004 at 191 hospitals across the US.
BNP blood tests had previously
been shown to have prognostic significance and help
diagnose patients with heart failure. However, it was
unknown whether BNP obtained upon admission, independent
of other risk factors, could help predict whether a
patient would have in-hospital complications or mortality.
The investigators determined that
in-hospital mortality rates closely corresponded with
BNP levels: less than 430 pg/ml carried a mortality
rate of 1.9%, between 430 and 839 pg/ml carried a mortality
rate of 2.8%, between 840 and 1,729 pg/ml carried a
mortality rate of 3.8%, while 1,730 pg/ml or more produced
a mortality rate of 6%.
HEAVYWEIGHT
MARKER
"There are many predictors of heart failure, but many
are not independent or as robust as BNP," says Dr Fonarow.
"Equally notable, BNP was predictive of mortality independent
of left ventricular ejection fraction, and worked equally
well in patients with either systolic or diastolic heart
failure."
Higher BNP levels were also predictive
of other clinical outcomes, such as the need for mechanical
ventilation, the length of the hospital stay and the
amount of time spent in the intensive care unit.
Dr Andrew Ignaszewski, head of
the division of cardiology at St. Paul's Hospital, Vancouver,
and co-author of the 2007 Canadian Cardiovascular Society's
(CCS) heart failure recommendations says Dr Fonarow's
findings are good news for Canada, where BNP testing
is only readily available in a handful of emergency
departments.
BNP
FOR BETTER OUTCOME
"A quick BNP check post-MI can quickly tell you who's
going to get in trouble and who's not," says Dr Ignaszewski.
"This is why the FDA approved the use of BNP as a marker
for stratification of patients post-MI. In Europe, BNP
testing has diagnostic footing equal to much more expensive
modalities, such as ECG or MRI. However, this latter
practice has not yet been incorporated anywhere in Canada."
He adds that, for the CCS, the definitive study showing
the need for BNP testing as a diagnostic or prognostic
tool has not yet been conducted.
"What you have right now is proof
positive that higher BNP results in worse outcomes,"
he says. "What needs to be shown now is that lowering
BNP levels results in better outcomes. The implications
could potentially be huge. Right now, heart failure
diagnosis is a lengthy process based on symptoms. If
BNP screening were available, it would be like other
biomarker tests — checking PSA to help diagnose
prostate cancer, for example. We could be diagnosing
people with heart failure way before they get into a
dangerous late stage."
Dr Fonarow agrees, saying that
the next step in his team's research is to prospectively
test whether BNP can be used to guide care, and whether
lowering BNP will translate to better clinical outcomes.
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